:”My fuel consumption when I re-filled the tank was 6.4L/100km (44mpg) with the cruise-control set at 90kph. You can’t do that with a petrol engine”

Oh yes you can and for vastly less.

For 1 trying feeding it with LPG, V8 like torque and power, less fuel cost than a silly smelly overpriced DIEsel.

You keep forgeting that euro and japper ULP’s are ALREADY VERY frugal on fuel use, check out the new Suzuki Alto for one.

But the real crusher is the current trend of “downsizing” the new 4cyl. Falcon will BEAT your figure, and with ease, a current 4L/6 of Hwy cycle will do around 7L/100km if also driven @ 90kmh and not hard use of the loud pedal.

Wonder how low this new EcoBoost can go on fuel use?

Lets see you i30 tow 2500kg trailer as Falcodores can! :-)

Generally speakin diesels peak power ends at 4000 rpm, which is when most petrol engines just start getting peak power(torque first and often power later)
calculate the amount of revs per annum a diesel does to a standard petrol and it would be close to a third less.

Also Diesel in Australia is only expensive for thanks to our inconsiderate government. Diesel IS a cheaper fuel, the Tax however placed on diesel is alot higher. If ya dad has a farm, get his diesel card, and not even olive oil would come close to the cost of running the vehicle.

Diesel prices are still taxed heavily on the back of the dirtier diesel from the past to offset carbon pollution.

I was told that its better to leave the Mazda in gear when going down hill as it totally shuts off fuel into the engine….

like just said, this tactic wouldnt apply to all vehicles, only those with the tech to adjust that.

my example of the carby was to show not every car would benefit even if some do. (now i understand some would)

i realise that modern engines dont have idle jets per se, i was saying that in taking it back to a basic motor form (carby sort of era).

the way i see it is some fuel would always have to be entering the engine.
and at the end of the day how much are you going to save reducing the idle suirt from full idle to half idle??
most of these tactics are a bit of a w*nk really.

who would take a car out of gear going down hill anyway??

The point is fuel injection systems allow all this, but it must be programmed, so not all cars would do that. With carbs the minimum amount of fuel used is controlled by the idle jets and the throttle, but as you can’t have no air going through the carb you can’t completely stop fuel be evaporated into the intake air from the idle jet, and so in that instance being in gear or neutral has no difference. With fuel injection, you can stop fuel being added to the intake charge, and hence if the ECU can measure that car acceleration due to gravity will equal or overcome pumping losses from the engine, then it could stop injection, until the throttle is opened slightly or the deceleration of the car is too high, which would indicate that you’ve reached the bottom of the hill.

As SuperCujo said, the computer knows when you are in gear and which gear you are in. It decides how much fuel and ignition timing it needs based on fixed tables of data.

When you close the throttle, the computer knows that the car is in gear and will -potentially- reduce fuel injection to levels BELOW what is required to idle the engine.

You, of course, feel this because the engine is trying to stop spinning (no/low fuel) but because it is still connected to the wheels it doesn’t just stop but applies a decelerative force. This is commonly referred to as engine braking.

I’m not sure about individual cars, but theoretically I can see how this could use less fuel than idling the engine down hills.

How much difference though? Anyone’s guess, but every one of the techniques helps a little.

Still, if you REALLY want to save fuel, buy a Diesel.